1. Field of the Invention
The present invention relates to splitters that preferably are, for example, used in cellular phones and more specifically relates to splitters in which a first band pass filter is connected to an antenna terminal and a second band pass filter is connected to the antenna terminal and has a pass band in a higher frequency range than the first band pass filter.
2. Description of the Related Art
In recent years, in cellular phones, signals have been transmitted and received using many communication schemes. Consequently, a splitter is connected to an antenna terminal.
For example, a splitter, which is illustrated in FIG. 5, is disclosed in International Publication No. WO 2005/088833. A splitter 1001 has an antenna terminal 1002. A band pass filter 1004, which has a relatively low pass band, is connected to the antenna terminal 1002 via a matching circuit 1003. The band pass filter 1004 is formed of a surface acoustic wave filter and an output terminal thereof is connected to a first terminal 1005.
A high pass filter 1006 is connected to the antenna terminal 1002 and an output terminal of the high pass filter 1006 is connected to a second terminal 1007. The cut off frequency of the high pass filter 1006 is located further toward the high frequency side than the pass band of the band pass filter 1004.
On the other hand, a high-frequency module that is equipped with a GPS reception filter and two band pass filters, which respectively receive two cellular bands, is disclosed in Japanese Unexamined Patent Application Publication No. 2006-108734. Here, the GPS reception filter and the two band pass filters are configured so as to be capable of being switched between using a switch.
In recent years, communication schemes employing various frequencies have been used together in cellular phones and so forth. In addition, for example, a GPS function has also been provided. For GPS and GLONASS, the transmission frequency band is 1.5 GHz to 1.6 GHz. In contrast, the transmission frequency band of WLAN is around 2.4 GHz according to IEEE802.11b and so forth. Therefore, for example, in the splitter 1001 illustrated in FIG. 5, a GPS signal can be received using the pass band of the band pass filter 1004 and a WLAN signal can be received with the high pass filter 1006.
However, the Band 7 transmission frequency band is located close to the frequency of the WLAN transmission frequency band, which is around 2.4 GHz. The Band 7 transmission frequency band is around 2.5 GHz to 2.6 GHz. Therefore, it is not possible to separate a WLAN signal from a Band 7 signal with the high pass filter 1006.
Therefore, for this purpose, it is necessary to connect a band pass filter 1008, whose pass band includes the WLAN transmission frequencies and is represented by the broken line in FIG. 5, downstream of the high pass filter 1006.
Moreover, even if such a band pass filter 1008 is connected, it is difficult to attain high steepness in an attenuated region adjacent to the WLAN pass band. The Band 7 transmission frequency band is very close to the WLAN transmission frequency band as described above. Therefore, in order to attain high steepness for an attenuated region at frequencies higher than the WLAN pass band, it has been necessary to further connect a band stop filter, which attenuates a signal of the Band 7 pass band, in addition to the band pass filter 1008. Therefore, there has been a problem in that the number of components and the cost are increased.
On the other hand, as described in Japanese Unexamined Patent Application Publication No. 2006-108734, connecting band pass filters for respective bands to an antenna terminal and switching between the filters using a switch has also been considered in order allow use of multiple bands. However, since a switch is necessary, increases in size and cost are incurred.